This invention relates to a light-sensitive silver halide photographic material, more specifically to a light-sensitive silver halide photographic material having a red-sensitive silver halide emulsion layer which has high sensitivity and also is improved in variation of photographic sensitivity caused by storing a raw sample for a long time and variation of gradation caused by light of a safelight.
Demands to a light-sensitive silver halide photographic material have become more strict year by year. In addition to strong demands of high sensitivity and high image quality (particularly excellent graininess and sharpness), low replenishing processing suitability for reducing environmental pollution and rapid processability to cope with demand of finishing within a short time have been strongly demanded. Most of these demands have been met by making a silver halide grain highly sensitive, and it is no exaggeration to say that high sensitivity of a silver halide grain is the largest task in this field of the art.
As one method of obtaining high sensitivity, it has been known that supersensitization is useful The supersensitization is described in "Photographic Science and Engineering", vol. 13, pp. 13 to 17 (1969), ibid, vol. 18, pp. 418 to 430 (1974), and "The Theory of the Photographic Process", edited by T. H. James, 4th edition, published by McMillan Co., 1977, p. 259, and it has been known that high sensitivity can be obtained by selecting a suitable sensitizing dye and a suitable supersensitizer.
In the prior art, as a supersensitizer for a red-sensitive spectral sensitizing dye, there have been known, for example, many compounds such as a stilbene, an azaindene, a mercapto hetero ring, a thiourea or a condensate of phenol and hexamethylenetetramine, and they have been disclosed in, for example, U.S. Pat. Nos. 2,875,058, 3,340,064, 3,457,078, 3,458,318, 3,615,632, 3,695,888 and 4,011,083, and Japanese Provisional Patent Publication No. 203447/1986.
However, it has been found that when a red-sensitive silver halide emulsion is supersensitized according to these prior techniques, variation deterioration of photographic sensitivity caused by natural storage is large, and further, when a light-sensitive material is exposed to light of a safelight before printing, gradation becomes soft. Since photographic characteristics are required to be uniform, aging stability in a raw sample of a light-sensitive photographic material is extremely important, and also safelight safety characteristics are extremely important from the standpoints of handling property of a light-sensitive material and prevention of lowering in quality of a finished print, so that a novel sensitizing method without bad influence on storage stability and safelight safety characteristics even when supersensitization is carried out has been demanded.